The present invention relates generally to a method of and apparatus for coating articles and, specifically, for coating metallic articles with plastic resin by a process which is known in the industry as powder coating. The articles to be coated are conveyed on a foraminous metallic conveyor through a spray booth. As the articles pass through the spray booth, they are coated with ionized particles of an uncured plastic resin. The resin particles are projected in the form of a spray for an electrode unit which charges and ionizes the particles. The articles to be coated are grounded through the metallic conveyor. The particles are attracted to the grounded article and deposited to all exposed surfaces of the article. The articles are then conveyed to a curing oven which cures or fixes the particles to the articles to form a permanent coating on the articles.
Since the metallic conveyor is also grounded, particles are attached to the conveyor so that the particles also become fixed to the conveyor when the articles are conveyed to the curing oven. Eventually, the conveyor becomes completely coated with plastic. This coating clogs the openings in the conveyor and insulates the conveyor from the articles so that the articles are not grounded and, therefore, do not attract the ionized resin particles. As the ground connection between the articles and the conveyor diminishes, the equality of the coating also diminishes to an unacceptable level.
In order from maintain an acceptable quality of coating on the articles, the conveyor must be replaced by a clean conveyor. This results in downtime and costly lost production. The coated conveyor must be cleaned by burning the coating. However, this creates two additional problems. The burning of the plastic coating requires consumption of energy and creates toxic fumes which must be contained. The equipment for performing both of these tasks and the energy which is required to perform both tasks add considerably to the cost of the coating operation.
Another problem with the existing coating systems is that all the particles which are deposited on the conveyor represent waste.
A still further problem with existing coating systems is that the surface of the article which is in contact with the conveyor is not completely covered with particles when it passes through the spray booth. Also, after the resin coating has been cured, the articles stick to the conveyor and have to be forcefully removed from the conveyor. This can damage the coating on the article and the surface which was in contact with the article has a rough and incomplete coating. The article can be run through this system again so that a different surface of the article rests on the conveyor so that the surface which was incompletely coated can be covered completely. However, the rough and complete coating on that surface prevents the surface from obtaining a uniform finish coating. These and other difficulties experienced with the prior art coating systems have been obviated by the present invention.
It is, therefore, a principle object of the invention to provide a system for coating articles by electro-static attraction of resin particles in which the particles are removed from the surface of the article which rests on the conveyor prior to curing of the resin so that a subsequent passing of the article through the coating system enables the uniform coating to be applied to the surface which was not coated in the first pass of the article through the system.
A further object of the present invention is the provision of a second conveyor which transports the articles through the curing oven after the articles have been coated with resin particles or powder and means for automatically transferring the powder coated articles from the first foraminous conveyor to the second conveyor.
Another object of the present invention is to provide means for removing the uncured resin powder from the foraminous conveyor after the conveyor passes through the spray booth.
A still further object of the invention is the provision of means for collecting the uncured resin powder which is removed from the foraminous conveyor and the articles for subsequently use.
With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.